Deformation twinning, i.e., twin nucleation and twin growth （or twin boundary migration, TBM） activated by impinged basal slip at a symmetrical tilt grain boundary in HCP Mg, was examined with molecular dynamics （M...Deformation twinning, i.e., twin nucleation and twin growth （or twin boundary migration, TBM） activated by impinged basal slip at a symmetrical tilt grain boundary in HCP Mg, was examined with molecular dynamics （MD） simulations. The results show that the {1^-1^-21}-type twinning acts as the most preferential mode of twinning. Once such twins are formed, they are almost ready to grow. The TBM of such twins is led by pure atomic shuffling events. A secondary mode of twinning can also occur in our simulations. The {112^-2} twinning is observed at 10 K as the secondary twin. This secondary mode of twinning shows different energy barriers for nucleation as well as for growth compared with the {1^-1^-21}-type twining. In particular, TBMs in this case is triggered intrinsically by pyramidal slip at its twin boundary.展开更多
High density nano-scale deformation twins were introduced in the surface layer of Cu sample by means of surface mechanical attrition treatment （SMAT） at room temperature. The Cu sample with deformation twins shows a...High density nano-scale deformation twins were introduced in the surface layer of Cu sample by means of surface mechanical attrition treatment （SMAT） at room temperature. The Cu sample with deformation twins shows a yield strength of about 470 MPa in tension tests. The significant strengthening may be attributed to the effective inhibition of slip dislocations by abundant twin boundaries.展开更多
By using Moire′ pattern formed by the double diffraction of precipitated V_4C_3 and matrix of γ-phase,the nature of the structure of the interface between precipitated V_4C_3 and matrix as well as the retarding effe...By using Moire′ pattern formed by the double diffraction of precipitated V_4C_3 and matrix of γ-phase,the nature of the structure of the interface between precipitated V_4C_3 and matrix as well as the retarding effect of V4C3 particles on the development of deformation twins have been investigated.It is shown that partially coherent interfaces exist between V_4C_3 and ma- trix.Twinning dislocations may transform into interfacial dislocations under external stress, and may move continuously through bypassing or cross-sliping.展开更多
Texture evolution of high-manganese twining-induced plasticity (TWIP) steels (Fe-16Mn-0.6C) during cold-rolling is studied by means of quantitative orientation distribution function (ODF)analysis.Thickness reductions ...Texture evolution of high-manganese twining-induced plasticity (TWIP) steels (Fe-16Mn-0.6C) during cold-rolling is studied by means of quantitative orientation distribution function (ODF)analysis.Thickness reductions of the specimens during cold-rolling are 10%,20%,30%,50% and 65%,respectively.Evolution of texture is of the Brass type,which is typical for low-stacking fault energy (SFE) materials.The contribution of deformation twinning to the development of texture is clearly illustrated by the monotonic increase of the twinned Cu component.In the present study,the deformation twinning was identified as significantly contributing to deformation up to the maximum reduction applied.These results are useful for the prediction and control of the texture in TWIP steels.展开更多
In austenitic Mn-steels with low stacking fault energy,the deformation twin is known to play an im-portant role in plastic deformation.Usually,the position grain boundary is preferred to observe and in-vestigate the f...In austenitic Mn-steels with low stacking fault energy,the deformation twin is known to play an im-portant role in plastic deformation.Usually,the position grain boundary is preferred to observe and in-vestigate the formation process of the deformation twin,while other suitable formation positions may be neglected.Here,high-resolution transmission electron microscopy is used to observe and characterize the formation of intracrystalline twins in 120Mn13 steel at the early stage of tensile plastic deformation at the atomic scale.The result shows that intracrystalline twins nucleate through overlapping stacking faults generated by three different perfect dislocations dissociating on consecutive{111}-type planes,which is different from twin nucleation mechanisms that have been proposed.Subsequently,they become large-sized intracrystalline twins or twin bands throughout the whole grain by twin nuclei growing themselves and connecting to adjacent twin nuclei or existing twins in the same growth direction.Intracrystalline twins are mainly formed in three positions,namely near the grain boundary,at the end or side of existing twins.The stacking fault sources of intracrystalline twins at different positions are different.展开更多
To satisfy the property requirements for biodegradable medical implants,Zn alloyed with low levels of Mg(≤0.8 wt%)has attracted increased research interest.In the present study,deformation twinning was observed in te...To satisfy the property requirements for biodegradable medical implants,Zn alloyed with low levels of Mg(≤0.8 wt%)has attracted increased research interest.In the present study,deformation twinning was observed in tensile tests and twinning appears to have an adverse impact on ductility.The profuse twinning in the as-cast Zn-Mg alloys accelerated crack growth in tension due to twinning impingement which caused local stress concentrations and initiates cracking.As-rolled Zn-Mg alloys have better ductility than their as-cast counterparts due to the inhibition of twinning by the refined Mg2Zn11 intermetallic phase and the finer grain size.展开更多
Based on its excellent tensile strength-ductility property combination,twinning-induced plasticity (TWIP) steel shows great potential in applications for structural components in automobile industry.The aim of this re...Based on its excellent tensile strength-ductility property combination,twinning-induced plasticity (TWIP) steel shows great potential in applications for structural components in automobile industry.The aim of this research is to investigate the corrosion resistance properties and corrosion mechanism under room temperature in TWIP steel.The influence of the deformation twin density on corrosion property was primarily considered by salt spray test.The specimens used in the investigation are as-annealed and as-deformed respectively.The microstructure and corrosion resistance property were characterized by scanning electron microscope (SEM),optical microscope (OM) and so on.There are some annealing twins distributed randomly in austenitic grains in the as-annealed specimen.After the specimen was subjected to tensile experiment,the density of the deformation twins increased sharply,which are different from the annealing twins in size and morphology.It was found that the corrosion potential of the as-annealed is lower than that of the as-deformed and the corrosion current density behaves contrarily.After immersed in 5% NaCl solution salt spray for 48h,the as-deformed showed a bit better than the as-annealed in corrosion resistance.With the time prolonged,the gap between the two specimens in corrosion resistance increased rapidly.The corrosion morphologies varied in color and shape.Further investigation,carried out by SEM and EDS,indicated that as-annealed and the as-deformed followed pitting corrosion and uniform corrosion mechanism respectively.The reason for the difference in corrosion mechanism is possibly the presence of the deformation twins.The deformation twins formed during the tensile test refine grains by way of segmentation.The twin boundaries largely belong to the coincidence site lattice (CSL),which is on lower energy state.It suggests that the twins not only play a role in strengthening,but also improve effectively the corrosion resistance in TWIP steel.展开更多
The deformation twins initiated in CrMnFeCoNi high entropy alloy at cryogenic temperature are experimentally studied. Under the external loading, a three-dimensional shear stress concentration originating from disloca...The deformation twins initiated in CrMnFeCoNi high entropy alloy at cryogenic temperature are experimentally studied. Under the external loading, a three-dimensional shear stress concentration originating from dislocation tangling at both the grain boundaries and twin boundaries could be formed, which promotes emission of partial dislocations from the planar defects and is thus considered to be the key factor for twin formation. A sympathetic nucleation mechanism is proposed to describe the nucleation behaviors of twins.展开更多
The effects of twin spacing and temperature on the deformation behavior of nanotwinned Al under tensile loading are investigated using a molecular dynamic（MD） simulation method.The result shows that the yield streng...The effects of twin spacing and temperature on the deformation behavior of nanotwinned Al under tensile loading are investigated using a molecular dynamic（MD） simulation method.The result shows that the yield strength of nanotwinned Al decreases with the increase of twin spacing,which is related to the repulsive force between twin boundary and the dislocation.The result also shows that there is no strain-hardening at the yield point.On the contrary,the stress is raised by strain hardening in the plastic stage.In addition,we also investigate the effects of stacking fault thickness and temperature on the yield strength of the Al nanowire.The simulation results indicate that the stacking fault may strengthen the Al nanowire when the thickness of the stacking fault is below a critical value.展开更多
Can aluminum generate deformation twins？ Contradictories exist among the experimental results, theoretical predictions, and molecular dynamics simulations. Our first-principles calculations based on the full-potentia...Can aluminum generate deformation twins？ Contradictories exist among the experimental results, theoretical predictions, and molecular dynamics simulations. Our first-principles calculations based on the full-potential linearly augmented plane wave method show that the bonding electron density of aluminum gathers at the tetrahedral interstices, and this specific electronic structure is in agreement with the experimental data from quantitative convergent-beam electron diffraction. In terms of this characteristic, the matching between the cohesive energy of local deformation twins with different thickness and global matrix can shed light on deformation twins in aluminum. This study may give a lane to insight into deformation twins in different metals.展开更多
Tensile behavior of an equiaxed-grained Fe-6.5 wt.%Si alloy,which was deformed intoφ6 mm bar by hot rotary swaging,was investigated at various temperatures(300–400℃)and stretching rates(0.42–1 mm/min).The results ...Tensile behavior of an equiaxed-grained Fe-6.5 wt.%Si alloy,which was deformed intoφ6 mm bar by hot rotary swaging,was investigated at various temperatures(300–400℃)and stretching rates(0.42–1 mm/min).The results revealed an enhancement in the intermediate-temperature tensile ductility after heat treatments.Deformation twinning was found in the equiaxed-grained Fe-6.5 wt.%Si bars during the tensile test,and heat treatments can enhance the deformation twinning.More twins can be observed in the necking areas than other regions.The high Schmid factor values above 0.4 after heat treatments demonstrated that deformation twinning can easily occur in the equiaxed-grained Fe-6.5 wt.%Si alloy.Higher deformation temperatures,higher strain rates,and larger degree of order suppressed the formation of deformation twinning,while the grain sizes had little effect on the deformation twinning.The twinning stress of the Fe-6.5 wt.%Si alloy increased with the increasing grain size,which did not agree with the Hall–Petch type relationship.The deformation twinning resulted in the improved ductility of the Fe-6.5 wt.%Si alloy.展开更多
An in situ study of twinning at crack tip in a TiAl-base alloy has been performed.The result shows that twinning with long shear vector(2/6) [112] can generate on(111) plane, even though usually it is very difficult t...An in situ study of twinning at crack tip in a TiAl-base alloy has been performed.The result shows that twinning with long shear vector(2/6) [112] can generate on(111) plane, even though usually it is very difficult to occur because of the high energy barrier. It was further shown that (1/6) [112](111) twinning is considerably easier to generate. Furthermore,(1/2)<110) ordinary dislocations were very active and dominated nearly the whole plastic zone, in spite of low Schmid factors. On the other hand, however <101) and (1/2) <112] superdislocations with higher Schmid factors can hardly be observed.展开更多
Synchrotron polychromatic X-ray microdiffraction（micro-XRD） was applied to study in situ deformation twinning of commercially AZ31（Mg-3Al-1Zn） strip subjected to uniaxial tension.The morphology and growth of twins...Synchrotron polychromatic X-ray microdiffraction（micro-XRD） was applied to study in situ deformation twinning of commercially AZ31（Mg-3Al-1Zn） strip subjected to uniaxial tension.The morphology and growth of twins were analyzed in situ under the load level from 64 to 73 MPa.The X-ray microdiffraction data,collected on beamline 12.3.2 at the Advanced Light Source,were then used to map an area of 396μm x 200μm within the region of interest.The experimental set-up and X-ray diffraction microscopy with a depth resolution allow the position and orientation of each illuminated grain to be determined at the submicron size.A list of parent grains sorted by crystallographic orientation were selected to examine their twinning behavior.The results depict twin variant selection,local misorientation fluctuation and mosaic spread for multi-twins within the same parent grain.As load increases,the amplitude of misorientation fluctuation along twin trace keeps increasing.This is attributable to the accumulation of geometrically necessary dislocations.展开更多
The structure characteristics of a2/γinterfaces and the features of deformation twins in a quasi-isothermal forged Ti-45Al-10Nb alloy were studied by highresolution transmission electron microscopy. Three types of st...The structure characteristics of a2/γinterfaces and the features of deformation twins in a quasi-isothermal forged Ti-45Al-10Nb alloy were studied by highresolution transmission electron microscopy. Three types of strain induced a2/γinterfaces and two types of strain induced twin boundaries were identified The most,important features are high density of ledges and the existence of I/3[111] Frank partial dislocation. Mechanisms for the formation these interfaces were proposed Two types of deformation twins were observed These deformation twins always start from the ledges it seems that ledges at interfaces are important features of interfacial structure for the mechanical behavior of alloys.展开更多
The influence of Y content on the grain-scale twinning behavior in extruded Mg−xY(x=0.5,1,5,wt.%)sheets under uniaxial tension and compression along the extruded direction was statistically investigated.An automatic t...The influence of Y content on the grain-scale twinning behavior in extruded Mg−xY(x=0.5,1,5,wt.%)sheets under uniaxial tension and compression along the extruded direction was statistically investigated.An automatic twin variant analysis was employed,based on large data sets obtained by electron backscatter diffraction(EBSD),including 2691 grains with 977 twins.The{1012}tension twinning(TTW)dominance and prevailing anomalous twinning behavior(Schmid factor(m)<0)under both tension and compression were found.The anomalous twinning behavior was more pronounced as Y content increased under tensile loading,indicating a promoted stochasticity of twin variant selection for more concentrated Mg−Y alloys.However,the trend for the Y-content dependent anomalous twinning behavior was opposite in compression.The fractions of the anomalous TTWs were found to be well correlated with the maximum Schmid factor(m_(max))values of basal slip and prismatic slip in the corresponding parent grains for compression and tension,respectively,indicating that twinning and dislocation slip might be closely related in the present Mg−Y alloys.展开更多
The nonequilibrium α2/γ interfacial structures have been studied using the conventional and high-resolution transmission electron microscope. The nonequilibrium γ/γ and α2/γ interfaces are important microstructu...The nonequilibrium α2/γ interfacial structures have been studied using the conventional and high-resolution transmission electron microscope. The nonequilibrium γ/γ and α2/γ interfaces are important microstructure features of hot-forged Ti-45Al-8Nb2.5Mn-0.05B alloys. The characteristics of these nonequilibrium interfacial boundaries include the frequent interfacial ledges and the deviation from the conventional orientation relationship {111}γ.展开更多
In the study,three 16Cr-25.5Ni-4.2Mo superaustenitic stainless steel weld metals with C contents of 0.082 wt%,0.075 wt%,and 0.045 wt%,were prepared to investigate the microstructural evolution and its effect on mechan...In the study,three 16Cr-25.5Ni-4.2Mo superaustenitic stainless steel weld metals with C contents of 0.082 wt%,0.075 wt%,and 0.045 wt%,were prepared to investigate the microstructural evolution and its effect on mechanical behavior.At a C content of 0.082 wt%,the microstructure of weld metal consisted of austenite,M_(6)C,and M_(23)C_(6),where M_(6)C was the main carbide.The number and average size of the M_(6)C carbides significantly decreased as the C content decreased.At a C content of 0.045 wt%,only a very small number of M_(6)C carbides were observed in the weld metal.For the tensile process,the number of deformation twins increased as the C content decreased,which introduced a stronger dynamic Hall-Petch effect,resulting in only a small decrease in the ultimate tensile strength of the weld metal.Meanwhile,the increase in deformation twins significantly enhanced the elongation of the weld metals.For the impact process,the impact energy increased from 204 to 241 J as the C content decreased.The crack initiation resistance was improved due to the reduction in M_(6)C carbide,which inhibited cracking at the interface of M_(6)C/matrix.Additionally,the crack propagation resistance was enhanced due to the increase in deformation twins,which consumed more impact energy.展开更多
To investigate the deformation twinning and the plastic anisotropy of the hexagonal-close-packed（HCP） single crystal, the crystal plastic constitutive model including slip and twinning deformation was established wi...To investigate the deformation twinning and the plastic anisotropy of the hexagonal-close-packed（HCP） single crystal, the crystal plastic constitutive model including slip and twinning deformation was established with finite element method based on crystal plasticity theory. The model was verified by test data. Newton-Raphson iteration method was developed with the stress components directly as the basic variables of iteration. The plastic deformation behavior of single crystal AZ31 alloy was analyzed numerically under monotonic tension and compression, respectively, in four different strain paths（i.e. along 〈2110〉, 〈 0110〉, 〈0001〉 and 〈0111〉） with this model. The stress-strain curves were obtained in the above paths. The numerical calculation results show that this crystal model is feasible to predict the activity of slip/twinning system and to describe the number of active twin variants, the types of dominant twin variants and twin intersection. Due to the polar nature of mechanical twinning in inelastic deformation of the material, the plastic behavior of the single crystal material is demonstrated to be notably anisotropic and high asymmetry.展开更多
Deformation twinning is known to be important in the acquisition of plasticity for hexagonal close-packed crystal structures,of great implication to the design and development of novel high-strength Mg alloys with enh...Deformation twinning is known to be important in the acquisition of plasticity for hexagonal close-packed crystal structures,of great implication to the design and development of novel high-strength Mg alloys with enhanced formability.Accurate understanding of deformation twinning necessitates critical mechanistic knowledge of the activation and selection of twins at nanoscale.In this work,considering polycrystalline Mg,we performed comprehensive molecular dynamics simulations to investigate deformation twinning under uniaxial tension and compression loading.An algorithm has been developed and implemented to identify the active twin variants of three operating twin modes during deformation.Sharp contrast between tension and compression loading in terms of twin patterns and twin growth was observed,attributed to difference in twin variant activation and twin-twin interaction under the two loading conditions.Furthermore,the critical role of Schmid factor in twin variant activation and selection has been elucidated,in good agreement with experimental observations.This study contributes critical insights towards advancing our understanding of the complex behaviors of deformation twinning in polycrystalline Mg.展开更多
Deformation twins and stacking faults were observed in nanostructure A1-Mg alloys subjected to high pressure torsion. These observations are surprising because deformation twinnings have never been observed in their c...Deformation twins and stacking faults were observed in nanostructure A1-Mg alloys subjected to high pressure torsion. These observations are surprising because deformation twinnings have never been observed in their coarse-grained counterparts under normal conditions. Experimental evidences are introduced on non-equilibrium grain boundaries, deformation twinnings and partial dislocation emissions from grain boundaries. Some of these features can be explained by the results reported from molecular-dynamics simulations of pure FCC metals. Special emphasis is laid on the recent observations of high density hexagonal and rhombic shaped nanostructures with an average size of 3 nm in the A1-Mg alloys processed by high pressure torsion. A possible formation process of these nanostructures is proposed based on molecular-dynamics simulations.展开更多
基金Project(2012CB932202)supported by the National Basic Research Program of ChinaProjects(50890174,50971088)supported by the National Natural Science Foundation of China
文摘Deformation twinning, i.e., twin nucleation and twin growth （or twin boundary migration, TBM） activated by impinged basal slip at a symmetrical tilt grain boundary in HCP Mg, was examined with molecular dynamics （MD） simulations. The results show that the {1^-1^-21}-type twinning acts as the most preferential mode of twinning. Once such twins are formed, they are almost ready to grow. The TBM of such twins is led by pure atomic shuffling events. A secondary mode of twinning can also occur in our simulations. The {112^-2} twinning is observed at 10 K as the secondary twin. This secondary mode of twinning shows different energy barriers for nucleation as well as for growth compared with the {1^-1^-21}-type twining. In particular, TBMs in this case is triggered intrinsically by pyramidal slip at its twin boundary.
基金This work was supported by the National Natural Science Foundation of China under grant No.50021101,50431010,50571096M0ST of China(Grant No.2005CB623604).
文摘High density nano-scale deformation twins were introduced in the surface layer of Cu sample by means of surface mechanical attrition treatment （SMAT） at room temperature. The Cu sample with deformation twins shows a yield strength of about 470 MPa in tension tests. The significant strengthening may be attributed to the effective inhibition of slip dislocations by abundant twin boundaries.
文摘By using Moire′ pattern formed by the double diffraction of precipitated V_4C_3 and matrix of γ-phase,the nature of the structure of the interface between precipitated V_4C_3 and matrix as well as the retarding effect of V4C3 particles on the development of deformation twins have been investigated.It is shown that partially coherent interfaces exist between V_4C_3 and ma- trix.Twinning dislocations may transform into interfacial dislocations under external stress, and may move continuously through bypassing or cross-sliping.
文摘Texture evolution of high-manganese twining-induced plasticity (TWIP) steels (Fe-16Mn-0.6C) during cold-rolling is studied by means of quantitative orientation distribution function (ODF)analysis.Thickness reductions of the specimens during cold-rolling are 10%,20%,30%,50% and 65%,respectively.Evolution of texture is of the Brass type,which is typical for low-stacking fault energy (SFE) materials.The contribution of deformation twinning to the development of texture is clearly illustrated by the monotonic increase of the twinned Cu component.In the present study,the deformation twinning was identified as significantly contributing to deformation up to the maximum reduction applied.These results are useful for the prediction and control of the texture in TWIP steels.
基金supported by the Key Projects of CRRC Technology Research and Development Plan(No.2022CXB195).
文摘In austenitic Mn-steels with low stacking fault energy,the deformation twin is known to play an im-portant role in plastic deformation.Usually,the position grain boundary is preferred to observe and in-vestigate the formation process of the deformation twin,while other suitable formation positions may be neglected.Here,high-resolution transmission electron microscopy is used to observe and characterize the formation of intracrystalline twins in 120Mn13 steel at the early stage of tensile plastic deformation at the atomic scale.The result shows that intracrystalline twins nucleate through overlapping stacking faults generated by three different perfect dislocations dissociating on consecutive{111}-type planes,which is different from twin nucleation mechanisms that have been proposed.Subsequently,they become large-sized intracrystalline twins or twin bands throughout the whole grain by twin nuclei growing themselves and connecting to adjacent twin nuclei or existing twins in the same growth direction.Intracrystalline twins are mainly formed in three positions,namely near the grain boundary,at the end or side of existing twins.The stacking fault sources of intracrystalline twins at different positions are different.
文摘To satisfy the property requirements for biodegradable medical implants,Zn alloyed with low levels of Mg(≤0.8 wt%)has attracted increased research interest.In the present study,deformation twinning was observed in tensile tests and twinning appears to have an adverse impact on ductility.The profuse twinning in the as-cast Zn-Mg alloys accelerated crack growth in tension due to twinning impingement which caused local stress concentrations and initiates cracking.As-rolled Zn-Mg alloys have better ductility than their as-cast counterparts due to the inhibition of twinning by the refined Mg2Zn11 intermetallic phase and the finer grain size.
基金the National Natural Science Foundation,P. R. China (51044007, 51001079)Scientific Research Plan of Shanxi Province of China (20090321072)National 863 plans projects (2007AA03Z555) for funding provided in support of this work
文摘Based on its excellent tensile strength-ductility property combination,twinning-induced plasticity (TWIP) steel shows great potential in applications for structural components in automobile industry.The aim of this research is to investigate the corrosion resistance properties and corrosion mechanism under room temperature in TWIP steel.The influence of the deformation twin density on corrosion property was primarily considered by salt spray test.The specimens used in the investigation are as-annealed and as-deformed respectively.The microstructure and corrosion resistance property were characterized by scanning electron microscope (SEM),optical microscope (OM) and so on.There are some annealing twins distributed randomly in austenitic grains in the as-annealed specimen.After the specimen was subjected to tensile experiment,the density of the deformation twins increased sharply,which are different from the annealing twins in size and morphology.It was found that the corrosion potential of the as-annealed is lower than that of the as-deformed and the corrosion current density behaves contrarily.After immersed in 5% NaCl solution salt spray for 48h,the as-deformed showed a bit better than the as-annealed in corrosion resistance.With the time prolonged,the gap between the two specimens in corrosion resistance increased rapidly.The corrosion morphologies varied in color and shape.Further investigation,carried out by SEM and EDS,indicated that as-annealed and the as-deformed followed pitting corrosion and uniform corrosion mechanism respectively.The reason for the difference in corrosion mechanism is possibly the presence of the deformation twins.The deformation twins formed during the tensile test refine grains by way of segmentation.The twin boundaries largely belong to the coincidence site lattice (CSL),which is on lower energy state.It suggests that the twins not only play a role in strengthening,but also improve effectively the corrosion resistance in TWIP steel.
基金supported by the National Natural Science Foundation of China(Nos.51872159 and 51572145)。
文摘The deformation twins initiated in CrMnFeCoNi high entropy alloy at cryogenic temperature are experimentally studied. Under the external loading, a three-dimensional shear stress concentration originating from dislocation tangling at both the grain boundaries and twin boundaries could be formed, which promotes emission of partial dislocations from the planar defects and is thus considered to be the key factor for twin formation. A sympathetic nucleation mechanism is proposed to describe the nucleation behaviors of twins.
基金Project supported by the National Natural Science Foundation of China (Grant No. 10902083)the Program for New Scientific and Technological Star of Shaanxi Province,China (Grant No. 2012KJXX-39)
文摘The effects of twin spacing and temperature on the deformation behavior of nanotwinned Al under tensile loading are investigated using a molecular dynamic（MD） simulation method.The result shows that the yield strength of nanotwinned Al decreases with the increase of twin spacing,which is related to the repulsive force between twin boundary and the dislocation.The result also shows that there is no strain-hardening at the yield point.On the contrary,the stress is raised by strain hardening in the plastic stage.In addition,we also investigate the effects of stacking fault thickness and temperature on the yield strength of the Al nanowire.The simulation results indicate that the stacking fault may strengthen the Al nanowire when the thickness of the stacking fault is below a critical value.
基金the support from the National Natural Science Foundation of China(NSFC)under grant Nos.51101162,51201165,and 51331007the financial support of"Hundred of Talents Project"by the Chinese Academy of Sciences
文摘Can aluminum generate deformation twins？ Contradictories exist among the experimental results, theoretical predictions, and molecular dynamics simulations. Our first-principles calculations based on the full-potential linearly augmented plane wave method show that the bonding electron density of aluminum gathers at the tetrahedral interstices, and this specific electronic structure is in agreement with the experimental data from quantitative convergent-beam electron diffraction. In terms of this characteristic, the matching between the cohesive energy of local deformation twins with different thickness and global matrix can shed light on deformation twins in aluminum. This study may give a lane to insight into deformation twins in different metals.
基金financially supported by the National Natural Science Foundation of China(Nos.51471031 and U1660115)the State Key Laboratory for Advanced Metals and Materials(No.2016Z-17)。
文摘Tensile behavior of an equiaxed-grained Fe-6.5 wt.%Si alloy,which was deformed intoφ6 mm bar by hot rotary swaging,was investigated at various temperatures(300–400℃)and stretching rates(0.42–1 mm/min).The results revealed an enhancement in the intermediate-temperature tensile ductility after heat treatments.Deformation twinning was found in the equiaxed-grained Fe-6.5 wt.%Si bars during the tensile test,and heat treatments can enhance the deformation twinning.More twins can be observed in the necking areas than other regions.The high Schmid factor values above 0.4 after heat treatments demonstrated that deformation twinning can easily occur in the equiaxed-grained Fe-6.5 wt.%Si alloy.Higher deformation temperatures,higher strain rates,and larger degree of order suppressed the formation of deformation twinning,while the grain sizes had little effect on the deformation twinning.The twinning stress of the Fe-6.5 wt.%Si alloy increased with the increasing grain size,which did not agree with the Hall–Petch type relationship.The deformation twinning resulted in the improved ductility of the Fe-6.5 wt.%Si alloy.
文摘An in situ study of twinning at crack tip in a TiAl-base alloy has been performed.The result shows that twinning with long shear vector(2/6) [112] can generate on(111) plane, even though usually it is very difficult to occur because of the high energy barrier. It was further shown that (1/6) [112](111) twinning is considerably easier to generate. Furthermore,(1/2)<110) ordinary dislocations were very active and dominated nearly the whole plastic zone, in spite of low Schmid factors. On the other hand, however <101) and (1/2) <112] superdislocations with higher Schmid factors can hardly be observed.
基金Project(DP140102355)supported by the Australian Research Council(ARC)Project supported by the China Scholarship Council(CSC)
文摘Synchrotron polychromatic X-ray microdiffraction（micro-XRD） was applied to study in situ deformation twinning of commercially AZ31（Mg-3Al-1Zn） strip subjected to uniaxial tension.The morphology and growth of twins were analyzed in situ under the load level from 64 to 73 MPa.The X-ray microdiffraction data,collected on beamline 12.3.2 at the Advanced Light Source,were then used to map an area of 396μm x 200μm within the region of interest.The experimental set-up and X-ray diffraction microscopy with a depth resolution allow the position and orientation of each illuminated grain to be determined at the submicron size.A list of parent grains sorted by crystallographic orientation were selected to examine their twinning behavior.The results depict twin variant selection,local misorientation fluctuation and mosaic spread for multi-twins within the same parent grain.As load increases,the amplitude of misorientation fluctuation along twin trace keeps increasing.This is attributable to the accumulation of geometrically necessary dislocations.
文摘The structure characteristics of a2/γinterfaces and the features of deformation twins in a quasi-isothermal forged Ti-45Al-10Nb alloy were studied by highresolution transmission electron microscopy. Three types of strain induced a2/γinterfaces and two types of strain induced twin boundaries were identified The most,important features are high density of ledges and the existence of I/3[111] Frank partial dislocation. Mechanisms for the formation these interfaces were proposed Two types of deformation twins were observed These deformation twins always start from the ledges it seems that ledges at interfaces are important features of interfacial structure for the mechanical behavior of alloys.
基金the National Natural Science Foundation of China(Nos.51401172 and 51601003)Fundamental Research Funds for the Central Universities,China(No.2682020ZT114)open funding of International Joint Laboratory for Light Alloys(MOE),Chongqing University,China。
文摘The influence of Y content on the grain-scale twinning behavior in extruded Mg−xY(x=0.5,1,5,wt.%)sheets under uniaxial tension and compression along the extruded direction was statistically investigated.An automatic twin variant analysis was employed,based on large data sets obtained by electron backscatter diffraction(EBSD),including 2691 grains with 977 twins.The{1012}tension twinning(TTW)dominance and prevailing anomalous twinning behavior(Schmid factor(m)<0)under both tension and compression were found.The anomalous twinning behavior was more pronounced as Y content increased under tensile loading,indicating a promoted stochasticity of twin variant selection for more concentrated Mg−Y alloys.However,the trend for the Y-content dependent anomalous twinning behavior was opposite in compression.The fractions of the anomalous TTWs were found to be well correlated with the maximum Schmid factor(m_(max))values of basal slip and prismatic slip in the corresponding parent grains for compression and tension,respectively,indicating that twinning and dislocation slip might be closely related in the present Mg−Y alloys.
文摘The nonequilibrium α2/γ interfacial structures have been studied using the conventional and high-resolution transmission electron microscope. The nonequilibrium γ/γ and α2/γ interfaces are important microstructure features of hot-forged Ti-45Al-8Nb2.5Mn-0.05B alloys. The characteristics of these nonequilibrium interfacial boundaries include the frequent interfacial ledges and the deviation from the conventional orientation relationship {111}γ.
基金supported by the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDA0410201)the Natural Science Foundation of Heilongjiang Province(No.TD2021E006)+1 种基金the Liaoning Provincial Doctoral Initiation Fund Project(No.2022-BS-008)the China Postdoctoral Science Foundation(No.2023T160654).
文摘In the study,three 16Cr-25.5Ni-4.2Mo superaustenitic stainless steel weld metals with C contents of 0.082 wt%,0.075 wt%,and 0.045 wt%,were prepared to investigate the microstructural evolution and its effect on mechanical behavior.At a C content of 0.082 wt%,the microstructure of weld metal consisted of austenite,M_(6)C,and M_(23)C_(6),where M_(6)C was the main carbide.The number and average size of the M_(6)C carbides significantly decreased as the C content decreased.At a C content of 0.045 wt%,only a very small number of M_(6)C carbides were observed in the weld metal.For the tensile process,the number of deformation twins increased as the C content decreased,which introduced a stronger dynamic Hall-Petch effect,resulting in only a small decrease in the ultimate tensile strength of the weld metal.Meanwhile,the increase in deformation twins significantly enhanced the elongation of the weld metals.For the impact process,the impact energy increased from 204 to 241 J as the C content decreased.The crack initiation resistance was improved due to the reduction in M_(6)C carbide,which inhibited cracking at the interface of M_(6)C/matrix.Additionally,the crack propagation resistance was enhanced due to the increase in deformation twins,which consumed more impact energy.
基金Projects(11272094,11072064)supported by the National Natural Science Foundation of ChinaProject(LGZX201101)supported by the Laboratory Center of Guangxi Science and Technology,ChinaProject(1074023)supported by the Science Foundation of Guangxi University of Science&Technology,China
文摘To investigate the deformation twinning and the plastic anisotropy of the hexagonal-close-packed（HCP） single crystal, the crystal plastic constitutive model including slip and twinning deformation was established with finite element method based on crystal plasticity theory. The model was verified by test data. Newton-Raphson iteration method was developed with the stress components directly as the basic variables of iteration. The plastic deformation behavior of single crystal AZ31 alloy was analyzed numerically under monotonic tension and compression, respectively, in four different strain paths（i.e. along 〈2110〉, 〈 0110〉, 〈0001〉 and 〈0111〉） with this model. The stress-strain curves were obtained in the above paths. The numerical calculation results show that this crystal model is feasible to predict the activity of slip/twinning system and to describe the number of active twin variants, the types of dominant twin variants and twin intersection. Due to the polar nature of mechanical twinning in inelastic deformation of the material, the plastic behavior of the single crystal material is demonstrated to be notably anisotropic and high asymmetry.
基金financial support from Natural Sciences and Engineering Research Council of Canada(NSERC RGPIN-2023–03628)H.C.also thanks the financial support from China Scholarship Council(201706050149)McGill Engineering Doctoral Award for financial support.
文摘Deformation twinning is known to be important in the acquisition of plasticity for hexagonal close-packed crystal structures,of great implication to the design and development of novel high-strength Mg alloys with enhanced formability.Accurate understanding of deformation twinning necessitates critical mechanistic knowledge of the activation and selection of twins at nanoscale.In this work,considering polycrystalline Mg,we performed comprehensive molecular dynamics simulations to investigate deformation twinning under uniaxial tension and compression loading.An algorithm has been developed and implemented to identify the active twin variants of three operating twin modes during deformation.Sharp contrast between tension and compression loading in terms of twin patterns and twin growth was observed,attributed to difference in twin variant activation and twin-twin interaction under the two loading conditions.Furthermore,the critical role of Schmid factor in twin variant activation and selection has been elucidated,in good agreement with experimental observations.This study contributes critical insights towards advancing our understanding of the complex behaviors of deformation twinning in polycrystalline Mg.
基金Project(50971087) supported by the National Natural Science Foundation of ChinaProject supported by the Research Council of Norway under the Strategic University Program on Light Metals Technology Projects(67692, 71594) supported by the Hungarian National Science Foundation
文摘Deformation twins and stacking faults were observed in nanostructure A1-Mg alloys subjected to high pressure torsion. These observations are surprising because deformation twinnings have never been observed in their coarse-grained counterparts under normal conditions. Experimental evidences are introduced on non-equilibrium grain boundaries, deformation twinnings and partial dislocation emissions from grain boundaries. Some of these features can be explained by the results reported from molecular-dynamics simulations of pure FCC metals. Special emphasis is laid on the recent observations of high density hexagonal and rhombic shaped nanostructures with an average size of 3 nm in the A1-Mg alloys processed by high pressure torsion. A possible formation process of these nanostructures is proposed based on molecular-dynamics simulations.
